The invention relates to a method for manufacturing compound material wafers, in particular silicon on insulator wafers, comprising the steps of: providing an initial donor substrate, forming an insulating layer over the initial donor substrate, forming a predetermined splitting area in the initial donor substrate, attaching the initial donor substrate onto a handle substrate, and detaching the donor substrate at the predetermined slitting are, thereby transferring a layer of the initial donor substrate onto the handle substrate to form a compound material wafer. The invention furthermore relates to a compound material wafer, in particular, a silicon on insulator wafer fabricated according to the previously mentioned method.
Compound material wafers, in particular the silicon on insulator (SOI) wafers, are semiconductor substrates which, in modern semiconductor devices, play a decisive role to ensure ever higher speed as smaller dimension are enabled. The process to fabricate such compound material wafers has, however, to satisfy at least two basic requirements. First, a good crystalline quality over essentially the entire surface of the wafer needs to be satisfied in the layered structure and, second the fabrication needs to be carried out without incurring excessive costs.
One way to satisfy the above mentioned requirements is the so called SMART-CUT® fabrication process in which a layer from a donor substrate is transferred onto a handle substrate. This is achieved by bonding the two substrates and detaching the donor substrate at a predetermined splitting area, which has previously been formed in the initial donor substrate. The predetermined splitting area is created beforehand by implanting atomic species, like hydrogen or rare gas ions into the donor substrate. This approach has the advantage that the donor substrate from which a layer is transferred from fabrication run to fabrication run, is reused several times. It appeared, however, that, from run to run, the crystalline quality of the transferred layer deteriorated. As a consequence a certain number of measures have been proposed to overcome this problem.
Japanese patent application JP 10114176 proposes additional process steps, like polishing the donor substrate, to remove the surface step at the edge of the wafer. This step is present after the transfer of a layer onto the handle substrate. Then a second finishing polishing step is carried out before the remainder of the donor substrate is reused as a as a new donor substrate in a subsequent fabrication run. US patent application 2003/029957 alternatively proposes, prior to polishing, additional heat treatment steps of the reclaimed donor wafer. It appeared, however, that even though improvements in the crystalline quality can be achieved by the additional process steps, the number of reuses still remained unsatisfactory low.
U.S. Pat. No. 6,211,041 does not deal with the reuse of donor substrates, but discloses an approach which consists in providing, right from the beginning, a silicon substrate with a low oxygen content preventing the creation of crystal defects. However, like for the other two methods, special additional steps are necessary beforehand to create the silicon substrate with reduced oxygen content and, in addition, the number of possible reuses of the donor substrate was still not satisfactory. Thus, improvements in these processes are necessary and desired.